During this year we have shown the practical usefulness of selenourea, the reagent that can be soaked into the native crystals of proteins to provide the strong anomalous diffraction signal of selenium used for solving novel crystal structures of macromolecules. Selenourea was in the previous year proposed to the biocrystallographic community by us as a simple and powerful vehicle for phasing diffraction data measured at synchrotron X-ray beam lines. This reagent allowed us to solve the crystal structure of XXX, one of the enzymes from the biosynthetic pathway of the amino acid histidine in plants. Within the methodological aspects of our activities, we conducted the analysis of non-crystallographic screw axes of different types occurring in protein crystal structures stored in the Protein Data Bank (PDB). In collaboration with Dr. Wlodawer (MCL in Frederick) and other colleagues the analysis various complexes of proteins with small molecular ligands was thoroughly analyzed and validated, often correcting the original suboptimal interpretation of results available in the literature and in the PDB. The unusual crystal structures of Z-DNA were analyzed, and interpreted as highly pseudosymmetric and six-fold merohedrally twinned specimens, not observed previously for these types of crystals. Within our activity directed at solving and interpreting crystal structures of proteins having biological or medical importance, we worked on selected model plant enzymes from the biosynthetic pathways of amino acids serine and histidine as well as aliphatic polyamines, which are not synthesized in animals and therefore may be relevant for development of agents active against various pathogens, with potential application in pharmacology or agriculture. The histidine pathway in the legume plant Medicago truncatula contain seven enzymes, catalyzing several reactions (some are bifunctional). All of them are expressed and five crystal structures are solved, interpreted and recently published. The rest are crystallized and the work on them continues. Four enzymes from the serine pathway are obtained and crystallized and structures of two of them fully characterized and published. The crystal structures of several enzymes involved in biosynthesis of polyamines putrescine spermine, spermidine and thermospermine were recently solved. The interpretation of the structure of thermospermine synthetase is published and work on other aminopropyltransferases continues.